Cardiac Pacemakers, Inc.

James T Bartelt

Scott W Carlson

A hand-held, portable, battery-powered test instrument for evaluating the performance of cardiac pacer devices prior to the implantation thereof and afterwards. To test R-wave sensitivity of a pacer device, a series of simulated R-waves, each of a predetermined greater amplitude, is applied to the pacer unit under test, each such simulated R-wave occurring at a time following a preceding pacer pulse sufficient to ensure that the pacer's refractory period has elapsed. This process is continued until a succeeding pacer pulse does not occur at the time it would otherwise be due, thus indicating that the R-wave had just reached the amplitude sufficient to cause the resetting of the pacer pulse generator. A count is maintained of the number of cycles needed to cause resetting of the pacer pulse generator and this value is displayed to indicate, in terms of voltage, the minimum amplitude of the R-wave just sufficient to result in pacer resetting.

Cardiac pacer testing system

Apparatus for measuring the amplitude of an adjustable width current or voltage impulse at a known time interval following the initiation of the impulse. During a first pulse duration, a counter is advanced with clock signals having a frequency f.sub.1. The total number of clock signals accumulated during the interval is then transferred into a downcounter which is arranged to be decremented during a second identical interval by a clock signal having a frequency n (f.sub.1). When the downcounter reaches zero, a strobe pulse is produced for enabling the analog measuring circuits which sample the amplitude of the current or voltage impulse being monitored. By selecting the value n, the sampling point can be shifted in time along the width of the pulse being measured. For example, for n=2, the amplitude of the voltage or current pulse being measured will be that occurring at the midpoint of the pulse.

Midpoint measuring circuit

An electronic test instrument for measuring the refractory interval of a demand-type cardiac pacer pulse generator. The normal pulse-to-pulse interval of the pacer under test is measured by accumulating regularly occurring timing signals in a first counter during the interpulse period. At a predetermined time after the occurrence of the first pulse defining the interval, a pseudo R-wave is generated and applied to the pacer under test. The next pulse-to-pulse interval is then measured in a second counter in a fashion similar to the first measurement and a test is made to determine if the second interval exceeds the first by a prescribed amount. If so, it is known that the pseudo R-wave was effective to reset the pacer's pulse generator. If not, the time of occurrence of the next pseudo R-wave is delayed by a further known amount and the operation is repeated over and over until an extension of the normal pulse-to-pulse interval is noted. When a point is reached where the pseudo R-wave is displaced in time from a first pacer pulse just enough to cause resetting of the pacer's pulse generator, a measure is made of the displacement interval and this value is visually displayed.

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Shoreview, MN, United States of America

James T Bartelt